Problem: $ A = \left[\begin{array}{rrr}1 & 1 & 2 \\ 1 & 0 & 2 \\ 1 & 2 & 0\end{array}\right]$ What is $ A^{-1}$ ?
Answer: $ = \left[\begin{array}{rrr}-2 & 2 & 1 \\ 1 & -1 & 0 \\ 1 & -\frac{1}{2} & -\frac{1}{2}\end{array}\right]$